The invention relates generally to computer touchscreens, and more particularly, to electrically conductive materials for touchscreens.
Since their introduction in the early 1970s, touchscreens have afforded alternatives to keyboards for certain computer applications. In many situations the keyboard and mouse are eliminated, because the touchscreen provides the user with access to the computer. Both resistive and capacitive touchscreens typically include a substrate, such as a glass panel, that is positioned over the face of a display, for example a liquid crystal display (LCD). The substrate includes an electrically conductive material on a surface thereof. The electrically conductive material defines an electrically conductive area on the substrate surface for accepting a user's inputs to the touchscreen. An insulating layer is positioned over the electrically conductive area to provide a surface for the user to touch to select the inputs.
In a resistive touchscreen, the insulating layer forms a portion of a cover sheet that includes a second electrically conductive material located over a surface of the insulating layer facing the substrate. The cover sheet is spaced from the substrate by a plurality of insulating dots such that the two electrically conductive materials are spaced apart. When the cover sheet is touched by a user, the two electrically conductive materials engage each other at the location of the user's touch. In capacitive touchscreens, the insulating layer is deposited directly on the electrically conductive material on the substrate.
The electrically conductive materials on both the substrate and the insulating layer are typically formed from indium tin oxide (ITO). ITO is often used because ITO generally provides good transparency for a given value of electrical conductivity, as is desired for some touchscreen applications. However, because the supply of indium is limited, ITO may be relatively expensive. Moreover, the increasing demand for indium may cause ITO to become even more expensive as the world supply diminishes. To replace ITO, several types of microscopic linear conductive elements (MLCEs), such as molecules of conductive polymers, carbon nanotubes and/or metal nanofibers, have been proposed for use in the electrically conductive material that is present on the substrate and/or on the cover sheets of touchscreens. However, at least some of such proposed MLCE materials do not match the transparency of ITO for a given electrical conductivity.
There is a need to increase the transparency of MLCE-based electrically conductive materials for touchscreens while maintaining the desired degree of electrically conductivity of the electrically conductive material.